HAX1‐related congenital neutropenia: Long‐term observation in paediatric and adult patients enrolled in the European branch of the Severe Chronic Neutropenia International Registry (SCNIR)

Summary HAX1‐related congenital neutropenia (HAX1‐CN) is a rare autosomal recessive disorder caused by pathogenic variants in the HAX1 gene. HAX1‐CN patients suffer from bone marrow failure as assessed by a maturation arrest of the myelopoiesis revealing persistent severe neutropenia from birth. The disorder is strongly associated with severe bacterial infections and a high risk of developing myelodysplastic syndrome or acute myeloid leukaemia. This study aimed to describe the long‐term course of the disease, the treatment, outcome and quality of life in patients with homozygous HAX1 mutations reported to the European branch of the Severe Chronic Neutropenia International Registry. We have analysed a total of 72 patients with different types of homozygous (n = 68), compound heterozygous (n = 3), and digenic (n = 1) HAX1 mutations. The cohort includes 56 paediatric (